The invention relates to a low tire pressure alarm system for vehicles such as trucks and cars to prevent accidents due to tire rupture or dangerously reduced tire pressures.
The system monitors tire pressure, actually air mass, in each of basically four active tires of a vehicle on a continuing basis. Each wheel has a self-contined unit including an air-mass or pressure sensor, cooperating with a power generator, and a transmitter, all integrated into a single easily insertable and replaceable unit.
Information furnished by the wheel units is transmitted to a common receiver when the vehicle is moving, which displays an "O.K." indication when all signals are received as normal; or a warning condition, e.g., with a flashing light; and an alarm if there is a failure in any of the wheels.
In addition to the basic two-level alarm capability to detect incipient failure, the system is also capable of providing individual indication of the tires to identify which one of them might fail or has already lost pressure or gas mass.
The present system is completely fail-safe. Failure of any transmitter of the wheel units triggers the alarm system, except when the vehicle is at a standstill, so that accidents can be prevented under all operating and weather conditions.
The sensor, is fastened to the inner periphery wall of the tire or alternatively to the outer rim of the steel wheel.
Tire inflation monitors have been known before, but they failed in one or more respects, so that the present invention is considered to constitute a major breakthrough and improvement over all hitherto known and used systems. There have been monitors that are locally applied to the wheels, however, there being no temperature evaluation devices for considering the temperature variations within the tire thus reflecting inaccurate pressure differentials.
While the scope of the desired patent protection will be defined later on in this application, the major inventive features are being set out here. First, it is important that air mass rather than pressure is used as an actuating agent in the sensors of the wheel units. No springs are used, and there is no inherent mechanical or other sluggishness. Since the air inside the device tends to have the same temperature as the air outside the device, the effect of temperature on pressure is substantially eliminated. This means that the inventive pressure or actuating mass sensor is completely compensated for cold days, hot days, hard running conditions, and the like outside influences.
Climatic conditions within the tire cavities are rather strenuous, such as water, ice, graphite, talcum powder, other agents, and primarily humidity. In the inventive sensor, everything takes place within a sealed cartridge. The mechanism cannot freeze, the electrical contacts cannot corrode, because the sealed sensor cartridge may contain dry air, nitrogen, or some other inert gas. The only moving part exposed to the outside is a flexible diaphragm that cannot be prevented from its relatively small motion by poor climatic conditions.
It is important to note that centrifugal forces arising from tire rotation have absolutely no effect on the measuring forces, the structural and directional arrangement being such that the relatively small mass and movemments are not affected by such outside forces.